This invention pertains generally to the field of x-ray spectroscopy and particularly to x-ray optics for spectroscopy.
The electron beam striking a sample in an electron microscope produces x-rays that are characteristic of the material of the sample that is impacted by the electron beam. Consequently, x-ray spectroscopes have been mounted to electron microscopes to analyze the x-rays emanating from the sample. X-rays at wavelengths characteristic of the sample are also produced by fluorescence from interaction of an x-ray beam with the sample, such as in x-ray microscopes. In energy dispersive spectroscopy (EDS), a solid state detector is positioned relatively close to the sample to collect x-rays emanating from the sample. The EDS detector receives and must detect x-rays of many wavelengths, and the resolution of the EDS system is limited by the resolution capability of the available solid state detectors.
In wavelength dispersive spectroscopy (WDS), the x-rays emanating from the sample are reflected from a wavelength dispersive element, typically a crystal or multi-layer diffracting element, which reflects the various wavelengths at specific angles. By changing the orientation of the diffracting element or of the position of the detector or both, the wavelength of x-rays that are incident upon the detector after redirection by the diffracting element can be selected, allowing relatively high precision spectroscopy with a capability of resolving relatively narrow peaks.
X-ray optics are employed in x-ray analytical instruments for focusing x-rays into high intensity spots, or for collimating x-ray beams. Exemplary applications for x-ray optics include microfluorescence, microdiffraction, tomography and lithography, and WDS. It has been pointed out that the use of an x-ray optic in a collimating configuration could provide enhanced detection sensitivity in WDS. WDS devices have been specifically designed to use grazing incidence collimating x-ray optics.
A few studies have appeared reporting the use of x-ray optics in applications using EDS. Focusing x-ray optics have been used on both the excitation and detection side of EDS systems. An x-ray microprobe which employs a monocapillary optic has been described. Polycapillary optics have been used to provide an intense convergent beam of x-rays from a microfocus x-ray tube to excite a sample for x-ray microfluorescence studies. A polycapillary optic has been used to increase the effective area of a microcalorimeter EDS. An intensity gain of nearly 300 (ratio of peak intensity with and without optic in place) with a fixed detector to sample distance of 66 mm was reported.
In accordance with the present invention, an x-ray optic is combined with an energy dispersive spectroscopy (EDS) detector to enhance the performance thereof. The x-ray optic may be a grazing incidence-type optic, a glass polycapillary-type x-ray optic, a hybrid grazing incidence/polycapillary-type optic, or any other known x-ray optic which may be employed in combination with an EDS detector in accordance with the present invention. Such an x-ray optic is employed to narrow the field of view of the EDS detector. This function of the x-ray optic is particularly applicable to improve EDS detection in broad beam spectroscopy applications, such as those employing environmental scanning electron microscopes (ESEM) and x-ray fluorescence.
In accordance with a preferred embodiment of the present invention, a compact grazing incidence x-ray optic is combined with a standard semi-conductor EDS detector. A grazing incidence optic (GIO) may be employed as a flux enhancing collimator for use with an EDS detector used to perform electron beam microanalysis. A GIO in combination with an EDS detector in accordance with the present invention provides substantial intensity gain for x-ray lines with energy below 1 keV. The GIO also provides a modest focusing effect, i.e., by limiting the field of view of the EDS detector, and introduces minimal spectral artifacts.
In accordance with the present invention, an x-ray optic employed in combination with an EDS detector may be employed as part of a conventional scanning electron microscope (SEM) or in broad beam spectroscopy applications such as in an ESEM, in which a specimen is analyzed in a relatively high ambient pressure, contrasted to normal SEMs operating under high vacuum, or spectroscopy employing x-ray fluorescence.
Further objects, features, and advantages of the invention will be apparent from the following detailed description when taken in conjunction with the accompanying drawings.